TEM studies of the microstructure of pressureless sintered copper

The microstructure of electrolytic copper powder was investigated during the sintering process by means of transmission electron microscopy and scanning electron microscopy. It is shown that the particle size, which is important for shrinkage, is much smaller than the size of the agglomerates obtained by sieving. The particles are polycrystalline with crystallite sizes of about 1 μm at the beginning of the sintering process. Both ex‐situ and in‐situ sintering were performed. During the sintering process the crystallite size increases. Recrystallization twinning is observed at temperatures above 400°C. The samples show local dislocation densities of about 10⁸ to 10⁹ cm⁻². The shrinkage velocities of Coble, Nabarro‐Herring, and dislocation creep are calculated and compared to the value experimentally obtained. The shrinkage velocities of all three transport mechanisms discussed here are in the same order of magnitude.